NAIROBI, Kenya (AP) -- Health officials battling the Ebola outbreak that has killed more than 4,500 people in West Africa have managed to limit its spread on the continent to five countries - and two of them appear to have snuffed out the disease. The developments constitute a modest success in an otherwise bleak situation. Officials credit tighter border controls, good patient-tracking and other medical practices, and just plain luck with keeping Ebola confined mostly to Liberia, Sierra Leone and Guinea since the outbreak was first identified nearly seven months ago.